This invention relates generally to photographic exposure control systems and, more particularly, to an exposure control system which is responsive to scene lighting in both ambient and flash modes of operation.
In U.S. Pat. No. 3,896,458, an automatic exposure control system responsive solely to scene light in ambient operation and additionally responsive to a subject distance in flash operation is described. In that arrangement, a shutter-diaphragm mechanism having a pair of reciprocally moving blade members simultaneously defines two correlated aperture values respectively controlling the scene light emitted to both the film plane and the camera photocell.
In the above-noted system, the shutter-diaphragm is driven from a closed position through enlarging aperture values with the photocell aperture, while small in comparison to the taking aperture, in a leading arrangement to the taking aperture so as to provide suitable anticipation of the final exposure value when the optical path is again blocked in accordance with a termination signal from the photocell network. In flash operation, the shutter-diaphragm is halted at predetermined positions in accordance with subject distance to select an operational aperture value for both the taking aperture and the photocell aperture. Compatible operation of the photoresponse is required for both modes of operation, but, additionally, because of the high light intensity reflected from the scene at near distances with flash exposure, it is important to provide very small photocell aperture values during initial stages of the blade opening. The latter requirement is complicated by factors inherent in forming small blade openings and in maintaining such openings in alignment during blade movement.
Consequently, it is an important object of this invention to provide a photographic exposure control system having improved photoresponsiveness.
It is another primary object of this invention to provide an improved automatic exposure control system suitable for both flash and ambient illumination at near subject distances.
Still another object of this invention is to provide a photographic diaphragm system having novel blade openings configured for providing relatively small, initial aperture values.